Organic conductor

ABSTRACT

The present invention provides an organic conductor comprising a deoxyribonucleic acid (DNA) and an electric charge-donating material bonded to the deoxyribonucleic acid, and an organic conductor comprising at least two DNAs; and an electric charge-transfer substance bonding to each base of the two DNAs.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic conductor having an improvedDNA conductivity which allows a DNA to be utilized as an electronicmaterial.

2. Description of the Related Art

A deoxyribonucleic acid (DNA) defined by Watson and Crick has a uniquedouble-helix structure consisting of pairs of four bases includingadenine, cytosine, guanine and thymine and ribose phosphate chains.Originally, a DNA is a substance, which constitutes a chromosome in anucleus of an organism, and has a function for replicating andtransmitting genetic information of a life by recording main geneticinformation in the base sequence of a DNA. The error rate in thetranscription of a DNA is very low, and is thought to be severalthousand times smaller than the error rate of an ordinary magneticmemory disk (10⁻⁴%). In addition, the thickness of a DNA is only about 2nm, but a DNA present in a nucleus of a cell has a length of aboutseveral meters when being extended and an extremely high dynamictoughness.

Since such a DNA has an almost one-dimensional geometric structure, itis being paid attention also as a low-dimensional transmittingsubstance. If a DNA can be employed on an electronic circuit, it canserve as a minute circuit element which can achieve an accumulationlevel exceeding that of a conventional silicon device circuit.Accordingly, the use of a DNA as an electronic device material isincreasingly being discussed, and attention is focused particularly onthe electric conductivity of the DNA. However, the level at which a DNAallows the electricity to flow is not known accurately, and is presentlystill being discussed.

As described above, the results of the prior studies have not beensuccessful in determining even whether a DNA is a conductor or not, andno accurate conductivity has been measured. Accordingly, there were notechnologies by which the electricity is supplied efficiently to a DNA.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide atechnology enabling a supply of electricity to a DNA which is essentialfor realizing an electronic device using the DNA.

According to such condition, the present inventor has studiedextensively, and finally discovered that an organic polymer formed bybinding an electric charge-donating material to a DNA has a highelectric conductivity and is stable chemically and thermally, therebyachieving the invention.

Thus, a first aspect of the invention provides an organic conductorcomprising a deoxyribonucleic acid (DNA); and an electriccharge-donating material bonded to the deoxyribonucleic acid (DNA).

A second aspect of the invention provides an organic conductorcomprising at least two DNAs; and an electric charge-transfer substancebonding to each base of the two DNAs.

An organic conductor of the invention allows a DNA for the first time tohave a conductivity, and enables the realization of an electric chargeseparation state in a single molecule, which is very useful industriallyfor the purpose of actuating a molecular level electronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of the structure of the presentinvention.

FIG. 2 is a diagram showing an example (A-1) of the structure of theinvention.

FIG. 3 shows the UV and visible light absorption spectra before andafter the reaction of a DNA and cis-platin.

FIG. 4 shows the infrared spectrum of a reaction product of cis-platinand DIDS.

FIG. 5 shows the infrared spectrum of DIDS.

FIG. 6 shows the infrared spectrum of cis-platin.

FIG. 7 shows the infrared spectrum of the reaction product of DIDS andCongo Red.

FIG. 8 shows the infrared spectrum of Congo Red.

FIG. 9 shows the infrared spectrum of the reaction product of a DNA,cis-platin, DIDS and Congo Red.

FIG. 10 is a graph showing the relationship of the currentdensity-voltage characteristic of the crosslinked construct (A-1).

FIG. 11 is a diagram showing the structure of the crosslinked construct(A-2).

FIG. 12 is a graph showing the relationship of the currentdensity-voltage characteristic of the crosslinked construct (A-2).

FIG. 13 is a graph showing the relationship of the current-voltagecharacteristic of the crosslinked construct (A-2).

FIG. 14 is a graph showing the current-voltage characteristic of λDNA.

FIG. 15 is a graph showing the current density-voltage characteristic ofG100 crosslinked construct and G0 crosslinked construct.

FIG. 16 is a graph showing the current density-voltage characteristic ofG100 crosslinked construct and G0 crosslinked construct.

FIG. 17 is a graph showing the current-voltage characteristic of G100crosslinked construct.

FIG. 18 is a graph showing the current-voltage characteristic of G0crosslinked construct.

FIG. 19 is a graph showing the current-voltage characteristic ofG100-cis-platin.

FIG. 20 is a graph showing the current-voltage characteristic ofG0-cis-platin.

FIG. 21 is a graph showing the thermogravimetric curve of the reactionproduct of a DNA, cis-platin, DIDS and Congo Red.

FIG. 22 is a graph showing the thermogravimetric curve of a DNA.

FIG. 23 is a graph showing the relationship between the guanineconcentration and the current.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a DNA imparted with an electric conductivity bybinding it with an electric charge-donating material. The DNA employedin the invention is not limited particularly, and may be any of asingle-stranded to quadruple-stranded DNAs and also may a DNA having atrifurcate or tetrafurcate branching structure. While the number of thebases is not limited, it is preferably 2 to 100,000.

An electric charge-donating material employed in the invention serves toinject a hole or an electron into a DNA. Since the electriccharge-donating material employed here bonds to the DNA, it ispreferable that the electric charge-donating material bonds specificallyto a base of the DNA. While an electric charge-generating substanceitself serves as an electric charge-donating material if the electriccharge-generating substance bonds directly to a base, the electriccharge-donating material preferably contains an electric charge-transfersubstance capable of bonding to a base and an electric charge-generatingsubstance when it is difficult for the electric charge-generatingsubstance to bond directly to the base.

When an electric charge-donating material bonds specifically to adesired base of a DNA, then the conductivity can be controlled based onthe base sequence constituting a DNA and the bonding site between DNAsand the number of the bondings can also be controlled. For example, acis-platin-containing electric charge-donating material described belowbonds specifically to guanine, whereby enabling the control as mentionedabove. The DNA employed here may be a naturally occurring one whosesequence, number or base position is known to a certain degree requiredfor its utilization, or may be an artificial one whose sequence isdesigned.

An electric charge-transfer substance employed in the invention is asubstance capable of transmitting a hole or electron generated in anelectric charge-generating substance to a DNA. The electriccharge-transfer substance may for example be a metal complex, andpreferably a platinum complex. Such a platinum complex is preferably acarcinostatic platinum complex (cis-platinum (II) diamine dichloride(hereinafter abbreviated as cis-platin), cis-[Pt(NH₃)₂Cl₄], trans-DDP,[Pt(dien)Cl]⁺, carboplatin, CHIP (iproplatin), DACCP, malonatoplatinumand the like as shown below.

An electric charge-generating substance may, for example, be an aminecompound, particularly one in which the number of amine groups is 1 to100 per molecule of the amine compound, and more preferably awater-soluble amine. Those preferred particularly are Congo Red,pararosanilin, thionine, porphyrin and the like as shown below.

When an electric charge-transfer substance capable of bonding to a basecannot be bonded directly to an electric charge-generating substance,then they may be bonded to each other via a crosslinking agent. Such acrosslinking agent is preferably a water-soluble crosslinking agent,particularly a water-soluble isothiocyanate represented by Formula 1(4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid disodium salt(hereinafter abbreviated as DIDS),4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonic acid disodium saltand the like), succinic acid imide ester represented by Formula 2(ethylene glycol-O,O′-bis(succinimidyl)succinate (hereinafterabbreviated as EGS).

While an organic conductor of the invention may be in a form obtainedsimply by binding an electric charge-donating material to adeoxyribonucleic acid (DNA), it may be in a form in which 2 or more DNAsare crosslinked with the electric charge-donating material. Thus, theform may be DNA-electric charge-donating material-DNA, or a repeatingstructure such as DNA-electric charge-donating material-DNA-electriccharge-donating material-DNA-. The number of DNAs in such a crosslinkingstructure may be 2 to 100,000.

The invention is further detailed by exemplifying an inventive organicconductor having a crosslinking structure. This has a structure shown inFIG. 1. The characteristics of the chemical substance can be obtained insuch a manner that a guanine base of a DNA is bonded to a metal complex,preferably the above-described carcinostatic platinum complex(cis-platin, cis-[Pt(NH₃)₂Cl₄], trans-DDP, [Pt(dien)Cl]⁺, carboplatin,CHIP (iproplatin), DACCP, malonatoplatinum and the like), followed by athiourea bond formation using a water-soluble crosslinking agent,preferably a water-soluble isothiocyanate represented by Formula 1(DIDS, or 4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonic aciddisodium salt and the like) or an amide bond formation using EGSrepresented by Formula 2, via which an electric charge-generatingsubstance such as an amine compound, preferably a water-soluble amine,particularly Congo Red, pararosanilin, thionine, porphyrin and the likedescribed above is bonded to the DNA.

A further description is made below with exemplifying a substanceDNA/cis-platin/DIDS/Congo Red/DIDS/cis-platin/DNA (hereinafterabbreviated as A-1) (see FIG. 2). When a DNA is reacted with cis-platin,the chlorine on cis-platin is cleaved to form a bond at the N7 positionof a guanine base of the DNA (Formula 3). Subsequently, —NH₃ ofcis-platin and N═C═S group (thioisocyanate group) of DIDS are reacted toform a thiourea bond (Formula 4). At the same time, Congo Red, which canform a similar thiourea bond, is reacted (Formula 5), whereby producingA-1 shown above (Formula 6).

This substance allows the electric charge to be separated in a Congo Redmolecule to form a hole which is transmitted by the conjugated doublebond and a phenyl group in DIDS, followed by an injection of the holespecifically to a guanine group of a DNA by means of cis-platin bondedto the guanine base of the DNA, whereby accomplishing the transmissionof the hole in the DNA molecule chain. The reasons why the hole canreadily be injected at the guanine base site of the DNA is the fact thatthe oxidation potential of the guanine is lower than those of otherthree bases (adenine, cytosine, thymine). The oxidation potential ofeach base, relative to hydrogen electrode potential, is 1.49 V forguanine, 1.96 V for adenine, 2.14 V for cytosine, 2.11 V for thymine asreported by C. A. M. Seidel et al. (Journal of Physical Chemistry,vol.100, pp.5541 to 5553, 1996, p.5544, Table 2). As a result, theconductivity of the substance of the invention can be improved.

Generally, the electric resistance of a DNA is extremely high, and theconductivity cannot be dramatically improved even if an organic dye orthe like capable of generating an electric charge in a molecule isintercalated. Nevertheless, it can be interpreted that when a hole isinjected specifically to a guanine base to increase the electric chargeconcentration in the DNA then the electric charge in the DNA istransferred, whereby allowing the current to run more easily. On theother hand, when the electric charge is an electron, the electron isinjected into cytosine or thymine.

Since A-1 has two bonding sites which are equivalent for all moleculesand which are also symmetrical chemically, it can form a complicatedcrosslinking structure using a DNA as a backbone chain. Thus, astructure: DNA/cis-platin/DIDS/Congo Red/DIDS/cis-platin/DNA can beconsidered. Such a structure allows the thermal resistance of thesubstance to be improved to give a thermal decomposition temperature ashigh as about 450° C. or higher under nitrogen atmosphere, wherebyhaving an extremely high chemical stability.

On the other hand, an ordinary conductive polymer such as apolyacetylene or polypyrrole becomes instable readily by an atmosphericoxidation, and requires a chemically instable iodine and the like as adopant for generating the conductivity. On the contrary, A-1 of theinvention does not require a dopant for generating the conductivity, isstable under atmosphere, and exhibits no change in the characteristicseven after being allowed to stand at room temperature under atmospherefor 1 month after production.

It is a matter of course that a substance forming no crosslinkingstructure can also be considered, such as a DNA/cis-platin/DIDS bondedat its tip to a monoamine dye, in which no crosslinking structure isformed and a fibrous DNA structure is preserved. The reaction is notlimited to a reaction only with DNAs, and a DNA molecule can be bondedto a protein molecule via cis-platin/DIDS/(diamine compound)/DIDS/.

Since Congo Red has an absorption wavelength of about 570 nm and givesalmost no fluorescence, it can be employed also as an electriccharge-generating material. Accordingly, the synthesized A-1 canconstitute an extremely stable photosensor. In addition, Congo Red is adyeing agent which stains an amyloid protein specifically, and thesynthesized A-1 can be employed also as an electronic sensor whichdetects many amyloid proteins having β sheet structures (β type prions).

A structure in which 2 or more DNAs are bonded via an electriccharge-transfer substance capable of bonding to a base or a structure inwhich such an electric charge-transfer substance capable of bonding to abase is bonded via a crosslinking agent has been proven to have aconductivity higher than that of a DNA itself. The electriccharge-transfer substance and the crosslinking agent mentioned here aresimilar to those described above. Those which can be exemplified includea substance having a DNA/cis-platin/DIDS/cis-platin/DNA structure, whichforms a crosslinking structure and has a conductivity higher than thatof a DNA itself.

EXAMPLES

The invention is further described in the following Examples which arenot intended to restrict the invention.

Example 1

The water employed was a super-pure water (having a resistance of 10¹⁸ Ωor higher) obtained by purification using a super-pure water producinginstrument MILLIQ manufactured by MILLOPORE. The DNA employed was abacteriophage λcl₈₅₇ Sam7-derived λDNA (TAKARA SHUZO Co., Ltd.). TheλDNA was dissolved at 0.4 mg/ml in a TE buffer (Tris: 10 mM, EDTA: 1 mM,pH=8). First, 1 ml of the λDNA buffer solution was mixed with 80 μl of a2.5 mg/ml aqueous solution of cis-platin (Sigma-Aldrich Co.). Then 301μl of a 1 mg/ml aqueous solution of DIDS (DOJINDO LABORATORIES) and 400μl of a 0.5 mg/ml aqueous solution of Congo Red (Wako Pure ChemicalIndustries, Ltd.) were added to the resultant mixture, and the mixturewas kept at 55° C. for 3 days. The formation of the crosslinkedconstruct represented by Formula 6 was identified on the basis of theresults described below. A naturally occurring DNA has the maximumabsorption wavelength of 260 nm in a UV and visible light absorptionspectrum, but it is known to undergo an about 10 nm red shift of themaximum absorption wavelength when a Pt complex is bonded (Journal ofthe American Chemical Society, 1980, Vol.102, pp.5565 to 5572, Chottardet al., p.5567, left column, line 8 from the bottom). FIG. 3 shows theUV and visible light absorption spectrum when a DNA was reacted withcis-platin. As evident from FIG. 3, the DNA itself exhibited the maximumabsorption at 260 nm, while that when reacted with cis-platin exhibitedthe maximum absorption at 270 nm. Thus, the maximum absorptionwavelength underwent the red shift by 10 nm. Based on these results, itwas proven that cis-platin was bonded to the DNA. FIG. 4 shows theinfrared absorption spectrum when DIDS was reacted with cis-platin. Whencomparing the infrared absorption spectrum of DIDS shown in FIG. 5 andthe infrared absorption spectrum of cis-platin shown in FIG. 6, it wasfound that the peak at 2140 cm⁻¹ derived from an N═C═S group disappearedwhile the absorption peak at 1302 cm⁻¹ derived from an N—C═S group newlyappeared. Based on these results, it was proven that cis-platin wasbonded to DIDS. FIG. 7 shows the infrared absorption spectrum when DIDSwas reacted with Congo Red. FIG. 8 shows the infrared absorptionspectrum of Congo Red. Based on the findings that the peak at 2140 cm⁻¹derived from an N═C═S group of DIDS disappeared while the thiourea bondpeaks at 1645 and 1545 cm⁻¹ were intensified, it was proven that DIDSwas bonded to Congo Red. Also based on the overall spectrum shown inFIG. 9 indicating that the peak at 2140 cm⁻¹ derived from an N═C═S groupof DIDS disappeared while the thiourea bond peaks at 1645 and 1545 cm⁻¹were intensified, the crosslinked construct (A-1) represented by Formula6 was proven to be formed.

To purify the crosslinked construct thus synthesized, ethanolprecipitation was conducted. 200 μl of the reaction solution was takenout into a sample tube, and 20 μl of a 3 mol/l aqueous solution ofsodium acetate and 400 μl of ethanol were added to and mixed thoroughlywith the reaction solution. After being allowed to stand at roomtemperature for 1 hour, the mixture was centrifuged at 4° C. and 13,200rpm for 30 minutes to separate the supernatant and the pellet. Thepellet recovered was dissolved again in 10 μl of super-pure water. Adrop of this aqueous solution was added by a microsyringe onto the goldelectrode formed on a glass substrate with the electrode distance of 10μm, and dried under nitrogen atmosphere overnight. As a result, a thinfilm of the sample was formed on the gold electrode.

The current-voltage characteristic of this sample thin film wasevaluated. The current-voltage characteristic was measured using pAMETER/DC VOLTAGE SOURCE 4140B (current detection sensitivity of 10⁻¹² A)manufactured by Hewlett Packard. The results are shown in FIG. 10. TheλDNA exhibited no detectable current, showing a resistance of 10 G Ω orhigher. On the other hand, the crosslinked construct showed 0.1 A/m²(5×10⁻¹ S/m) at 2 V, indicating an improved DNA conductivity accordingto the present method.

Example 2

400 μl of a 0.32 mg/ml λDNA buffer solution was mixed thoroughly with 12μl of a 5 mg/ml aqueous solution of cis-platin and 300 μl of a 1 mg/mlaqueous solution of DIDS, and kept at 55° C. for 3 days. Similarly toExample 1, the crosslinked construct (A-2) shown in FIG. 11 wasconfirmed to be generated based on the UV and visible absorptionspectrum and infrared absorption spectrum. To purify the crosslinkedconstruct thus synthesized, ethanol precipitation was conducted. 200 μlof the reaction solution was taken out into a sample tube, and 20 μl ofa 3 mol/l aqueous solution of sodium acetate and 400 μl of ethanol wereadded to and mixed thoroughly with the reaction solution. After beingallowed to stand at room temperature for 1 hour, the mixture wascentrifuged at 4° C. and 13,200 rpm for 30 minutes to separate thesupernatant and the pellet. The pellet recovered was dissolved again in10 μl of super-pure water. A drop of this aqueous solution was added bya microsyringe onto the gold electrode formed on a glass substrate withthe electrode distance of 10 μm, and dried under nitrogen atmosphereovernight. As a result, a thin film of the sample was formed on the goldelectrode. The current-voltage characteristic was evaluated, and theresults obtained are shown in FIG. 12. However, the crosslinkedconstruct synthesized here gave no detectable current with the electrodedistance of 10 μm, showing a resistance of 10 G Ω or higher.Accordingly, the electrode distance was reduced and then thecurrent-voltage characteristic was measured. The measurement wasconducted employing Dual Probe AFM (Japanese Patent ApplicationNo.2001-006284). The results are shown in FIG. 13. As a result, when theelectrode distance was reduced to about 50 nm, a current of about 4 nAwas detected at 3 V. As shown in FIG. 14, a naturally occurring λDNAallows no current to be detected even with the electrode distance of 50nm, suggesting that this method can impart a DNA with a conductivitywithin 50 nm.

Example 3

Four single-stranded DNAs (hereinafter referred to as ssDNAs) of 120bases represented by SEQ. ID. Nos. 1 to 4 were designated ssDNA1 tossDNA4, respectively, each of which was synthesized by a phosphoramiditemethod using a DNA synthesizer Expedite 8909 manufactured by AppliedBiosystems. There was complementarity of the base sequence betweenssDNA1 and ssDNA2 and between ssDNA3 and ssDNA4, and a double-strandedDNA can be formed via hydrogen bonds by hybridization. The hybridizationwas effected by mixing respective ssDNAs at the molar ratio of 1:1 andthe resultant mixture was kept at 97° C. for 5 minutes and then cooledto room temperature slowly. After forming a double-stranded DNA by thehybridization, ethanol precipitation was conducted for purification. Adouble-stranded DNA formed from ssDNA1 and ssDNA2 was designated G0,while a double-stranded DNA formed from ssDNA3 and ssDNA4 was designatedG100. All regions other than the regions of 10 base pairs from the bothterminals of G0 consisted of adenine-thymine base pairs. On the otherhand, all region other than the regions of 10 base pairs from the bothterminals of G100 consisted of guanine-cytosine base pairs. Using G100and G0, a crosslinked construct similar to that in Example 1 wassynthesized by the following procedure. 1 ml of a 0.4 mg/mldouble-stranded DNA buffer solution was mixed with 80 μl of a 2.5 mg/mlaqueous solution of cis-platinum (II) diamine dichloride. Then 301 μl ofa 1 mg/ml aqueous solution of DIDS and 400 μl of a 0.5 mg/ml aqueoussolution of Congo Red were added to the mixture, and the resultantmixture was kept at 55° C. for 3 days. 200 μl of the reaction solutionwas taken out into a sample tube, and 20 μl of a 3 mol/l aqueoussolution of sodium acetate and 400 μl of ethanol were added to and mixedthoroughly with the reaction solution. After being allowed to stand atroom temperature for 1 hour, the mixture was centrifuged at 4° C. and13,200 rpm for 30 minutes to remove the supernatant and recover thepellet. To purify the crosslinked construct thus synthesized, ethanolprecipitation was conducted. 200 μl of the reaction solution was takenout into a sample tube, and 20 μl of a 3 mol/l aqueous solution ofsodium acetate and 400 μl of ethanol were added to and mixed thoroughlywith the reaction solution. After being allowed to stand at roomtemperature for 1 hour, the mixture was centrifuged at 4° C. and 13,200rpm for 30 minutes to separate the supernatant and the pellet. Thepellet recovered was dissolved again in 10 μl of super-pure water. Adrop of this aqueous solution was added by a microsyringe onto the goldelectrode formed on a glass substrate with the electrode distance of 10μm, and dried under nitrogen atmosphere overnight. As a result, a thinfilm of the sample was formed on the gold electrode.

-   SEQ. ID. No.: 1-   Length of sequence: 120-   Type of sequence: Nucleic acid-   Strandedness: Single-stranded-   Topology: Linear-   Molecular type: Synthesized DNA-   Sequence description:

CACTGCATAT AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA 60AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA CAATCGTATC 120

-   SEQ. ID. No.: 2-   Length of sequence: 120-   Type of sequence: Nucleic acid-   Strandedness: Single-stranded-   Topology: Linear-   Molecular type: Synthesized DNA-   Sequence description:

GATACGATTG TTTTTTTTTT TTTTTTTTTT TTTTTTTTTT TTTTTTTTTT TTTTTTTTTT 60TTTTTTTTTT TTTTTTTTTT TTTTTTTTTT TTTTTTTTTT TTTTTTTTTT ATATGCAGTG 120

-   SEQ. ID. No.: 3-   Length of sequence: 120-   Type of sequence: Nucleic acid-   Strandedness: Single-stranded-   Topology: Linear-   Molecular type: Synthesized DNA-   Sequence description:

CACTGCATAT GGGGGGGGGG GGGGGGGGGG GGGGGGGGGG GGGGGGGGGG GGGGGGGGGG 60GGGGGGGGGG GGGGGGGGGG GGGGGGGGGG GGGGGGGGGG GGGGGGGGGG CAATCGTATC 120

-   SEQ. ID. No.: 4-   Length of sequence: 120-   Type of sequence: Nucleic acid-   Strandedness: Single-stranded-   Topology: Linear-   Molecular type: Synthesized DNA-   Sequence description:

GATACGATTG CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC 60CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC CCCCCCCCCC ATATGCAGTG 120

The results of the evaluation of the current-voltage characteristics ofG100 crosslinked construct and G0 crosslinked construct are shown inFIGS. 15 and 16. When the electrode distance was 10 μm, G0 crosslinkedconstruct gave no detectable current, while G100 crosslinked constructgave 4 A/m² (10 S/m) at 4 V (FIG. 15) with the maximum level of 3800A/m² (10⁴ S/m) being given at 4 V (FIG. 16). The current-voltagecharacteristic of G100 crosslinked construct by Dual Probe AFM is shownin FIG. 17. G100 crosslinked construct gave 5 nA at 1 V with theelectrode distance of 500 nm. The current-voltage characteristic of G0crosslinked construct by Dual Probe AFM is shown in FIG. 18. GOcrosslinked construct gave no detectable current even with the electrodedistance of 150 nm.

Comparative Example 1

Cis-platin was added to the double-stranded DNA G0 and G100 synthesizedin Example 3 by the following procedure. 1 ml of a 0.4 mg/mldouble-stranded DNA buffer solution was mixed with 80 μl of a 2.5 mg/mlaqueous solution of cis-platin, and the mixture was kept at 55° C. for 3days. For the purification, ethanol precipitation was conducted. 200 μlof the reaction solution was taken out into a sample tube, and 20 μl ofa 3 mol/l aqueous solution of sodium acetate and 400 μl of ethanol wereadded to and mixed thoroughly with the reaction solution. After beingallowed to stand at room temperature for 1 hour, the mixture wascentrifuged at 4° C. and 13,200 rpm for 30 minutes to remove thesupernatant and recover the pellet. Similarly to Example 1, cis-platinwas proven to be added to the DNA on the basis of the UV and visiblelight absorption spectrum. The results of the evaluation of thecurrent-voltage characteristic using Dual Probe AFM are shown in FIGS.19 and 20. As a result, no detectable current was obtained simply byadding cis-platin to G100 and G0, and it was found that the product hada resistance of 10G Ω or higher.

Example 4

A DNA isolated from salmon sperm (Wako Pure Chemical Industries, Ltd.)was employed. First, the purification was conducted by ethanolprecipitation. 200 μl of a 2 mg/ml DNA TE buffer solution was taken outinto a sample tube, and 20 μl of a 3 mol/l aqueous solution of sodiumacetate and 400 μl of ethanol were added to and mixed thoroughly withthe buffer solution. After being allowed to stand at room temperaturefor 1 hour, the mixture was centrifuged at 4° C. and 13,200 rpm for 30minutes to remove the supernatant. 200 μl of 70% ethanol was added tothe remaining pellet, and the mixture was centrifuged at 4° C. and13,200 rpm again for 5 minutes to remove the supernatant and recover theprecipitating purified DNA. 5.6 ml of a 2 mg/ml aqueous solution ofpurified DNA was mixed thoroughly with 2.24 ml of a 2.5 mg/ml aqueoussolution of cis-platinum (II) diamine dichloride and 2.24 ml of a 1mg/ml aqueous solution of DIDS and the mixture was kept at 55° C. for 3days. 200 μl of the reaction solution was taken out into a sample tube,and 20 μl of a 3 mol/l aqueous solution of sodium acetate and 400 μl ofethanol were added to and mixed thoroughly with the reaction solution.After being allowed to stand at room temperature for 1 hour, the mixturewas centrifuged at 4° C. and 13,200 rpm for 30 minutes to remove thesupernatant and recover the pellet. The thermal decompositiontemperature of the crosslinked construct thus synthesized was determinedusing a Perkin Elmer thermal analyzer TGA-7. The resultantthermogravimetric curve is shown in FIG. 21. The thermal decompositiontemperature was found to be 450° C. On the other hand, the thermaldecomposition temperature of the DNA was 250° C. as shown in FIG. 22.

Example 5

The currents of the crosslinked construct in Example 1, G100 and G0 inExample 3 were compared with each other by the method employed inExample 1. The results are shown in FIG. 23. The point at the bottom onthe left represents the result of G0 in Example 3, the middle linerepresents the result of the crosslinked construct in Example 1 and theline at the top on the right represents the result of G100 in Example 3.Based on this figure, we found that the current was increased inresponse to the concentration of guanine in a DNA.

1. An organic conductor comprising a deoxyribonucleic acid (DNA) strand;and an electric charge-donating material bonded to the deoxyribonucleicacid (DNA) strand, wherein the electric charge-donating materialcomprises an electric charge-transfer substance, which is a platinumcomplex, that bonds to a base of the DNA strand and an electriccharge-generating substance, wherein the electric charge-transfersubstance and the electric charge-generating substance are bonded toeach other via a crosslinking agent; wherein the electriccharge-generating substance is an amine compound that is one or moreselected from Congo Red, pararosanilin and thionine.
 2. The organicconductor of claim 1, wherein the electric charge-donating material isbonded specifically to a desired base of the DNA strand.
 3. The organicconductor of claim 1, wherein the electric charge-donating material is asubstance having a reduction potential that oxidizes a base of a DNAstrand.
 4. The organic conductor of claim 1, wherein the platinumcomplex is cis-platinum (II) diamine dichloride.
 5. The organicconductor of claim 1, wherein the number of amine groups of the aminecompound is 1 to 100 per molecule of the amine compound.
 6. An organicconductor comprising a deoxyribonucleic acid (DNA) strand; and anelectric charge-donating material bonded to the deoxyribonucleic acid(DNA) strand, wherein the electric charge-donating material comprises anelectric charge-transfer substance, which is a platinum complex, thatbonds to a base of the DNA strand and an electric charge-generatingsubstance, wherein the electric charge-transfer substance and theelectric charge-generating substance are bonded to each other via acrosslinking agent; and wherein the crosslinking agent is4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid disodium salt (DIDS) orethylene glycol-O,O′-bis(succinimidyl) succinate (EGS).
 7. The organicconductor of claim 1, wherein the DNA strand includes 2 to 100,000bases.
 8. The organic conductor of claim 1, wherein the DNA strand is asingle-stranded to quadruple-stranded DNA.
 9. The organic conductor ofclaim 1, wherein the DNA strand has a trifurcate or tetrafurcatebranching structure.
 10. The organic conductor of claim 1, wherein atleast two DNA strands have a structure in which they are crosslinkedwith the electric charge-donating material.
 11. An organic conductorcomprising at least two DNA strands; and an electric charge-donatingmaterial bonded to the two deoxyribonucleic acid (DNA) strands, whereinthe electric charge-donating material comprises an electriccharge-transfer substance, which is a platinum complex, that bonds toeach base of the two DNA strands and an electric charge-generatingsubstance; and wherein the electric charge-generating substance is anamine compound that is one or more selected from Congo Red,pararosanilin and thionine.
 12. The organic conductor of claim 11,wherein the electric charge-transfer substance bonds specifically to adesired base of the DNA strands.
 13. The organic conductor of claim 11,wherein the platinum complex is cis-platinum (II) diamine dichloride.14. An organic conductor comprising at least two DNA strands; and anelectric charge-transfer substance, which is a platinum complex, bondingto each base of the two DNA strands, wherein the electriccharge-donating material comprises an electric charge-transfersubstance, which is a platinum complex, that bonds to each base of thetwo DNA strands and an electric charge-generating substance; wherein theelectric charge-transfer substance and the electric charge-generatingsubstance are bonded to each other via a crosslinking agent; and whereinthe crosslinking agent is 4,4′-diisothiocyano-2,2 ′-stilbenedisulfonicacid disodium salt (DIDS) or ethylene glycol-O,O′-bis(succinimidyl)succinate (EGS).